Since reserves of metals such as rare metals are limited, it is important to recycle resources effectively. Furthermore, toxic metals such as heavy metals should be collected from waste fluids discharged from factories etc.
A method using algae has been proposed as a method for adsorbing metal ions in a solution. For example, a method for adsorbing ions of rare earth elements using chlorella etc. has been proposed (JP H6-212309 A). Furthermore, it has been reported that a macromolecule extracted from Aphanothece sacrum, which is a freshwater cyanobacterium, adsorbs metal ions (International publication No. WO 2008/062574).